In a power chuck or the like it is frequently necessary to convert a rotation into linear movement. This is done, for instance, to open or close the jaws of a chuck. Such a converter typically has coaxial input and output elements, the former being axially displaceable and the later rotatable. Rollers or the like engaged between them perform the necessary movement conversion.
German patent document 3,937,448 Hubert Bald et al uses balls as motion-converting members. Thus the rotatable elements are axially braced via these balls on an axially non-displaceable support member. Thus the support element must move both axially and rotationally.
The use of such a converter on rapidly rotating lathes creates several problems, namely:
1. To reduce throw the length and diameter must be as small as possible.
2. The converter must be able to transmit and convert considerable forces.
3. No matter what the position of the device its center of mass must not move to prevent throw and vibration.
4. Large mechanical advantage must be obtained even in a system capable of transmitting considerable force, even in a relatively small unit.
Furthermore it is necessary that the converter be of relatively simple and, therefore, inexpensive construction. In particular the screwthread guides that are essential in such a device much be designed so that they can be manufactured inexpensively.